1. Field of the Invention
The present invention relates to a display device having an image capture function, and an imaging method.
2. Related Art
A liquid crystal display device has an array substrate on which signal lines, scanning lines, and pixel TFTs (thin film transistors) are disposed, and drive circuits that drives the signal lines and the scanning lines. Based on recent advancement and development of integrated circuit technology, a process technique of forming a part of the drive circuits on the array substrate is in practical use. With this technique, the total liquid crystal display device can be made light, thin and compact, to enable the display device to be widely used for various kinds of portable devices such as portable telephones and notebook computers.
A display device having image capture function, which has photoelectric conversion elements to capture images disposed on the array substrate, is proposed (For example, see Japanese Patent Application Nos. 2001-292276 and 2001-339640).
The conventional display device having the image capture function changes charges of capacitors connected to the photoelectric conversion elements according to the amount of light received by the photoelectric conversion elements, to detect voltages at both ends of the capacitor, thereby capturing an image.
Recently, a technique of forming pixel TFTs and drive circuits on the same glass substrate according to a polycrystalline silicon (i.e., polysilicon) process has been developed. It is possible to easily form the photoelectric conversion elements in each pixel by using the polysilicon process.
In order to detect gradations of a picked-up image in the display device having an image capture function, a method of picking up images by changing the pickup time in stages, and combining the picked-up images to finally obtain one image is available.
According to this method, however, the picked-up image finally obtained is not correctly subjected to a gamma adjustment, and therefore, has poor display quality. There is also a risk that the obtained image has much noise, depending on characteristics of the photoelectric conversion element. There is also a risk that a setting of an image capture condition is complex.
The present invention has been achieved in the light of the above problems, and has an object of providing a display device having an image capture function with excellent display quality and with little noise. It is another object of the present invention to provide an imaging method capable of picking up image based on a simple condition setting.